Polygonal cutting insert

ABSTRACT

A polygonal indexable cutting insert has a chip breaker with a backwall arranged in a sinuous path with the portion approaching the corner having a shallower slope than the main portion.

This application is a continuation-in-part application of U.S. pending application Ser. No. 081,266, now U.S. Pat. No. 4,787,784 entitled "Polygonal Cutting Insert", filed Aug. 3, 1987.

BACKGROUND OF THE INVENTION

The present invention relates to disposable cutting inserts which may be detachably mounted on a tool holder for cutting a work piece. Cutting inserts of this type are generally made of cemented metal carbide and are formed by pressing and sintering techniques.

In the type of cutting inserts referred to herein, it is desirable to have an indexable insert which presents a positive rake cutting edge to the working piece.

U.S. Pat. No. 3,885,281 to Stambler describes an insert having both longitudinally curved and transversally curved channels along the side edges of the insert which meeting at the corners of the insert. Also each corner of the insert, V-shaped shallow grooves are depressed into the merging portions of the deeper longitudinal channels to provide chip control for shallow depth cuts.

U.S. Pat. No. 3,786,541 to Lundgren relates to a cutting insert having chip breakers in two stages wherein the cutting edge and the associated chip breaker describe a curve of a particular description.

U.S. Pat. No. 3,786,540 describes an insert having chip control groove extending along a side surface. The width of the groove describes a compound curve such that the width varies along the length of the side.

U.S. Pat. No. 3,399,442 to Jones describes an insert having chip control groove along the entire outer edge comprising an inner and outer region. The outer region is concave in cross-section.

U.S. Pat. No. 4,335,984 to Zweekly describes an insert having a plurality of breaking depressions in the chip breaker surface adjacent to the cutting corner.

U.S. Pat. No. 4,273,480 describes a succession of chip control recesses formed on the cutting face at the outer periphery along the cutting edge. The chip control recesses are generally spherical and may intersect or contact each other as well as the cutting edge.

U.S. Pat. No. 4,215,957 discloses depressions which are generally rectangular with inner corners spaced from the cutting edge.

SUMMARY OF THE INVENTION

As the workpiece is cut, the chip which is removed flows over the cutting edge and downwardly and inwardly along a descending wall portion. The chip next encounters a floor and then an ascending wall which directs the chip upwardly and outwardly. Chip breakers of the prior art include a variety of strategically located islands, bumps, and angles in a variety of configurations which tend to radial deform the flowing chip. This deformation tends to cause breakage of the chip. Heretofore, chip breakers have not concentrated on being oriented to the cutting edge in such a way so as to present an advantageous angle with the cutting edge to deflect the chip in an axial direction or a direction parallel with the cutting edge actually performing the cutting. In the present invention, the chip breaker angle with the cutting edge results an efficient chip-breaking action so as to provide chip control of the chip in an axial direction. More specifically, due to the configuration of the chip breaker, the chip tends to deflect in an axial direction toward the center.

U.S. patent application Ser. No. 081,266 now U.S. Pat. No. 4,787,784 as referred to above relates an insert having a backwall surface extending in a sinuous path. More specifically, a polygonal indexable cutting insert comprises a pair of substantially parallel spaced-apart faces and peripheral side surfaces normal to said parallel faces. The faces on the side surfaces are joined to form corners. The pair of cutting edges extend away from each corner substantially within the plane of a respective face. Each cutting edge extends between a corner and its respective adjacent corners. A floor surface is substantially parallel to a respective face surface and spaced downwardly toward the center of the insert therefrom. A ramp surface extends downwardly from a respective cutting edge to the floor surface to form a positive rake insert. A backwall surface is spaced rearwardly of the cutting edge and extends upwardly from a respective floor surface to a respective face surface. The backwall surface extends in a sinuous path from a corner of the insert to a position intermediate the corners in a manner tending to deflect chips in a direction parallel to the cutting edge and toward the center of the insert.

The present invention is an improvement of the aforementioned application and includes a backwall of reduced slope at the corners for enhancing nose stability by reducing uncontrolled deterioration of the corners during cutting.

It is an object of the present invention to obviate one or more disadvantages of the prior art.

Other and further objects of the present invention will be apparent to one of ordinary skill in the art from reading of the detailed specification.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top-elevational view of an insert of the parent application.

FIG. 2 is a sectional view along section 2--2 of FIG. 1;

FIG. 3 is a detailed sectional view of a chip breaker along a portion of line 2--2 of FIG. 1;

FIG. 4 is a detailed view in section of another portion of the chip breaker along line 4--4 of FIG. 1.

FIG. 5 is a top-elevational view of another insert of the parent application.

FIG. 6 is a top elevational view of insert of the present invention having a modified back wall at the corner.

FIG. 7 is a side elevational view in section along a section 6--6, a corner bisector of the insert of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, the cutting insert 15 has substantially parallel faces 17,19 with peripheral side surfaces 21-24 normal to the parallel faces 17,19. The faces 17,19 are joined with side surfaces 21-24 to form eight corners at the junctions. One corner 25 is at the juncture of face 17 and side surfaces 21 and 24. The remaining corners are similarly formed. A pair of cutting edges 27,29 extend away from corner 25 substantially within the plane of a face 17. Cutting edge 27 extends from corner 25 to an adjacent corner 26. Similarly, each of the respective cutting edges extend between adjacent corners.

For purposes of the following discussion, inwardly or the inward direction is toward the center of the insert while outwardly or the outward direction is in a direction away from the center of the insert. With reference to chip flow over a cutting edge, the radial direction is generally perpendicular to the cutting edge while the axial direction is parallel to the cutting edge.

Continuing with a discussion of FIGS. 1 and 2, the insert 15 is provided with a pair of floor surfaces 33,35. Each floor surface 33,35 is spaced inwardly from the respective face surfaces 17,19. The chip breaker, as shown in FIG. 2 and in detail in FIG. 3, includes a respective ramp surface 37 which extends downwardly from a respective cutting edge 21 to the floor surface 33 and a backwall 41 which slopes upwardly from the floor surface 33 to the face surface 17. Each cutting edge has associated therewith a similarly formed chip breaker.

As illustrated in FIG. 1, the ramp surface 37 extends inwardly a predetermined distance from a respective cutting edge 27,29 and forms a land of uniform width extending entirely around the periphery of the insert 15. Typically, each ramp surface includes very small flatland portion 45 extending inwardly therefrom so as to strengthen the cutting edge. In FIG. 4, flatland portion 45 is shown at a 5 degree angle with the face surface 17. Preferably, the ramp surface 37 extends downwardly from the cutting edge at an angle of 15 to about 25 degrees, and more preferably at an angle of about 20° as shown in FIG. 4 at B.

Preferably, the ramp surface 37 extends downwardly a suitable distance respective face surface 17 to the floor surface 33. The floor surface 33 should be sufficiently deep so as to change the direction of chip flow. The directional change enhances the tendency of the chip to break.

The backwall surface 41 extends intermediate to respective floor surface 33 and a respective face surface 17. As shown in FIG. 1, the backwall surface 41 forms a sinuous path along a direction parallel to the cutting edge. A chip flowing over the cutting edge 27 down the ramp surface 37 and along the floor surface 33 encounters the backwall surface 41. At the junction of the floor surface 33 and backwall surface 41, a flowing chip encounters a backwall 41 which functions to deflect the chip in an outward direction away from the floor surface 33 and toward the parallel face 17. Due to the sinuous shape of the backwall 41, the chip tends to flow and be guided in the direction parallel to the cutting edge 27 and away from each of the corners 25,26. More specifically, the backwall extends from a position closely adjacent a corner to the intermediate position in such a manner that chips tend to be deflected toward inwardly along a direction parallel to the cutting edge. The tendency of chips to flow in a direction parallel with the cutting edge toward the center of the insert is achieved by having the backwall have a leg extending at an acute angle with the cutting edge. As chips flow over the cutting edge, they tend to be deflected toward the center of the insert.

The sinuous backwall 41 forms a wave pattern undulating toward and away from the ramp surface 37. Starting at a point closely adjacent corner 26, the backwall 41 undulates toward the center of the insert and then outwardly toward the ramp surface 37 before undulating toward the center. Progressing from corner 26 to 25 in a direction parallel to the cutting edge 21, FIG. 1 shows an embodiment utilizing four undulations one of which is illustrated at 51. The backwall 41 includes at least two undulations positioned between each corner, preferably from 3 to 5 undulations, and more preferably 4 undulations. The embodiment illustrated in FIG. 1 shows four undulations while the embodiment shown in FIG. 5 illustrates five undulations.

Undulation 51 is representative of the undulations forming the backwall 41. Undulation 51 includes an inner portion 53 and an outer portion 55. A pair of leg portions 57,59 connect the inner portion of undulation 51 to a respective outer portion 55. Progressing in a direction parallel to the cutting edge 21 from corner 26 to the center of the insert as represented by center line 63, the respective legs of the respective undulations are alternately longer and then shorter than the next adjacent leg. For example, leg 59 is longer than adjacent leg 51 which in turn is shorter than adjacent leg 61 and which in turn is longer than the next leg.

As illustrated in FIG. 1 and in FIG. 5, the inner portions of the undulations such as shown at 53 are curved or arcuate while the outer portions adjacent the cutting edge 21 as shown at 55 are flat sections. The respective outer portions adjacent the respective corners are illustrated as curved sections. The purpose of the abrupt flat section closely adjacent the cutting edge is to impart an immediate change of direction to a chip.

In operation, the chip breaker of the present invention tends to influence the flow of the chip in both a radial and axial direction. The greater distance a chip travels before striking a backwall, the greater the radial curve while the shorter the distance the tighter the radial curve. Due to this effect, the undulations tend to enhance the tendency of chips to be directed toward the center of the insert.

FIG. 5 illustrates an embodiment utilizing five undulations 61 between corners 63 and 65. The inner portion 67 of the backwall 69 is directly adjacent the ramp surface 71 at one position adjacent the corner 65. Although both FIGS. 5 and 1 illustrate an indexable insert having four sides, it is contemplated that triangular inserts may be included within the scope of the present invention together with other variations apparent to one of ordinary skill in the art.

FIG. 6 illustrates an embodiment of the present invention wherein the slope of the backwall at respective corners is modified. Although a triangularly-shaped cutting insert is shown at 71 in FIG. 6, the following description applies to other polygonal inserts typically used for cutting. The insert 71 includes a sinuous backwall 73 which undulates toward the center of the insert and then outwardly toward the ramp surface 75 before undulating toward the center. Preferably, the main portion of the backwall 77 intermediate the corners slopes upwardly from the floor 79 to the face 81 at a substantially constant angle. Preferably, the angle which is shown as angle C in FIG. 4 is relatively steep, an angle of from about 30 to about 40 degrees and more preferably at an angle of about 35 degrees.

The following description of modified corner 83 applies to the remaining corners of the polygonal. Corner 83 is bisected by center line 85. At the corner 83, the main portion of the backwall 73 forms a pair of complementary backwall portions 85, 87 which extend on opposite sides of the bisector or center line 85 toward corner 83. The complementary backwall portions 85, 87 preferably have the predetermined uniform slope as hereinbefore discussed. The bridging backwall portion 89 which joins and extends intermediate the complementary backwall portions 85, 87 extends outwardly closely adjacent the ramp surface 75.

A substantial portion of the bridging backwall portion 89 slopes upwardly from the floor 79 at a gradual angle of from about 5 to about 12 degrees. This angle which is shown in FIG. 7 as angle D is relatively shallow. Most preferably, angle D is about 8 degrees. In FIG. 7, the bridging or modified backwall portion 89 includes a first section 93 and second section 95 which have a slope corresponding to the main portion of the backwall 77. The first section 93 forms a juncture between the gradual sloping portion of the bridging portion 89 and the floor 79. The second section 95 forms a juncture between the gradual sloping portion of the bridging portion 89 and the face surface 81.

It has been found that reducing the slope of the backwall 73 at the corner results in enhanced nose stability by reducing uncontrolled deterioration of the corners during cutting. 

We claim:
 1. A polygonal indexable cutting insert comprising a pair of substantially parallel faces and peripheral side surfaces normal to said parallel faces,said faces and said side surfaces being joined to form corners, a pair of cutting edges extending away from each corner substantially within the plane of a respective one of said faces, a pair of floor surfaces, each floor surface being substantially parallel to a respective face and spaced downwardly therefrom, a ramp surface extending downwardly from a respective cutting edge to said floor surface whereby said insert has a positive rake, a backwall surface joining a respective floor surface and respective face surface and extending in a sinuous path from a position closely adjacent a respective corner inwardly and outwardly in a manner tending to deflect chips toward the center of said insert, said sinuous path comprising from three to five undulations, said backwall surface having a relatively shallow slope at the respective corners and a relatively steep slope intermediate said corners, said steep slope being at an angle of from about 30 to about 40 degrees and said shallow slope being at an angle of from about 5 to about 12 degrees, said sinuous path extends from a position closely adjacent a corner inwardly toward the center of the insert and outwardly toward the cutting edge, each undulation includes a curved portion near the center of the insert and a pair of outwardly extending leg portions successive legs being alternately longer and then shorter when progressing from a corner to the center of the insert in a direction parallel to the cutting edge. 